1. Field of the Invention
This invention relates to a binocular stereoscopic microscope which enlarges an observation area viewed through both eyes of the observer.
2. Description of the Prior Art
This type of binocular stereoscopic microscope K may for example comprise, as shown in FIG. 12, a main observing optical system 1, an auxiliary sub-observing optical system 2 (detailed drawing omitted) which branches off from the main observing optical system 1, and an electronic camera system 3 (detailed drawing omitted) which also branches off from the main observing optical system 1.
Referring to FIG. 12, the main observing optical system 1 comprises a left-hand/right-hand pair of observing optical systems 1a, 1b. The left-hand optical system 1a comprises an objective lens 10, magnifying lens 11, beam splitter 12, imaging lens 13, porroprism 14 (erecting prism), diamond-shaped prism 15, field diaphragm 16 and eyepiece 17 in that order. In the figure, H houses the objective lens 10, magnifying lens 11 and beam splitter 12.
This porroprism 14 comprises a rectangular prism 14a on the incidence side, an intermediate rectangular prism 14b and a rectangular prism 14c on the emergence side. The microscope parts from this porroprism 14 to the eyepiece 17 are housed in an eyepiece tube B.
The rectangular prism 14a on the incidence side is fixed. The eyepiece tube B is free to rotate about a reflection axis 0 of the rectangular prism 14a as shown by the arrow 18, and the diamond-shaped prism 15 is free to rotate about an incidence axis 01 as shown by the arrow 19.
The observing optical system 1b has the same composition as the observing optical system 1a, so its description will be omitted, parts of the system 1b corresponding to parts of the system 1a being referred to by the same symbols with dashes ('). The sub-observing optical system 2 branches off from the beam splitter 12, and the electronic camera optical system 3 branches off from the beam splitter 12'.
In the aforesaid construction, the optical parts from the intermediate rectangular prisms 14b, 14b' to the eyepieces 17, 17', may be rotated about the reflection axes 0, 0' so as to vary the height of the eyepieces 17, 17'. Further, by rotating the diamond-shaped prisms 15, 15' about the incidence axes 01, 01', the interoptic axis distance of the eyepieces 17, 17' may be varied. The operator observes a subject OP via these observing optical systems 1a, 1b.
This type of binocular stereoscopic microscope is widely used in engineering and medicine. Its purpose is not only to magnify a subject, but also to permit fine precision operations to be performed.
A binocular stereoscopic microscope is therefore required to allow the user (operator) to perform operations easily. For example, it should provide a suitable magnification, have a wide visual field so as to permit rapid alignment, and allow the operator to work in a comfortable position.
FIG. 14 shows such a binocular stereoscopic microscope K used for performing ophthalmic surgery. In this example, an operator F is looking down at an angle of 45.degree., but if the operator is short, his eyes (eye point P) will be at a lower position than that shown in the figure.
In such a case, it would be desirable to move the microscope K downwards, however as the distance between the microscope K and the observation area OP of the patient (not shown) is very small, it is actually impossible to move the microscope down.
The eyepiece tube B housing the optical parts from the intermediate rectangular prisms 14b, 14b' to the eyepieces 17, 17' was therefore rotated downwards about the reflection axes 0, 0' so as to reduce the elevation of the eyepiece tube B, and thereby move the operator's eye point P downwards.
However, as the porroprisms 14, 14' are disposed above the beam splitters 12, 12' and the imaging lenses 13, 13', there was a limit to how much the elevation of the eyepiece tube B could be reduced so as to move the operator's eye point P downwards.
To solve this problem, the eyepiece tube B could be disposed so that it rotated up and down about an axis at the side of the holder H.
However, if this arrangement were adopted, the dimensions of the binocular stereoscopic microscope increase in a front-back direction, and if the elevation of the eyepiece tube B is low, the operator's eye point P has to move further back than the microscope K. The operator's reaching distance RD, i.e. the distance from the observation area OP (undergoing surgery) to the eye point P, therefore increases.
FIG. 15 shows an example of the use of a binocular stereoscopic microscope K to perform a surgical operation wherein the microscope is horizontal. As it is impossible to reduce the elevation angle of the eyepiece tube B, the reaching distance RD from a part of a patient A undergoing surgery, i.e. the observation area OP, to the eye point P, increases.
Conventionally, therefore, the operator had to extend his arms to perform surgical procedures, and if the operator was of small stature, he occasionally could not reach the part of the patient to be operated upon.